Hitchcocks Forum

I've been reading all the good advice and tips on this forum for quite a while now, and I'm hoping that somebody with more experience than myself might be able to help me. I've managed to strip the spark plug thread on my Electra!

Would I be able to use a steel insert to repair it, or would this not allow the plug to cool properly (and maybe cause detonation)? Which would the best insert be for an aluminium cylinder? Any help would be much appreciated.

Yes you can fit a Helicoil or similar insert. It will have no effect on plug or its performance. Indeed as you will now be screwing a steel plug body into a steel thread it could be argued that in engineering terms you will have a better fitting item and almost no chance of stripping it again. You can buy a kit from Tracy Tools in Devon, normal disclaimers, and their kit includes a drill bit which allows you to drill and retap in one single process. It is possible to drill, tap and refit a helicoil insert without removing the head, but I would not recommend it as you are likely to drop the break off tang into the engine. If you do decide to take a chance on this just remember to grease the tap well so that the swarf you generate can be captured. So simply remove the head, drill and fit the insert and refit the head. Simples. Seriously it really is that simple. At least with an Enfield you only have the one insert to fit. The last time I did this was on a Honda 400/4 and took the opportunity to do all 4 plugs, but in reality it still didn't take more than 10 minutes. HTH.

If you really do want to do the job without removing the head, rotate the engine onto the firing stroke so both valves are shut then have the piston set about half inch or so BTDC. Grease up a length of rag cut to about a 1" wide strip and push this into the head. Then pump in a good decent amount of grease to sit on top of the rag. After the job ihas been completed as Mike explains, rotate the engine fully to TDC. The wad of grease will be pushed out of the plug hole taking with it most of any dropped swarf, then fish out the greasy rag with long nose pliers where any remaining debris will be sticking on to it. Any remaining grease will burn out very quickly after starting. Have I done this myself? Answer...NO...but that is how I WOULD do it, if time was the essence and I didn't want to remove the head.

Just to emphasise that the grease filling should be reach up to the bottom of the spark plug hole.

I think we should mention that our hosts supply a kit to do this as well. Would I take the head off? - well it would depend on what milage the bike's done. If it's at all due for the valves to be lapped in it would make sense to take the head off. I had mine off at 8500 miles and the valves did benefit from lapping. If you helicoil it, be very very carefull from then on as the helicoil way try to come out with the plug in future. Perhaps an iridium plug might be a good idea as they do tend to last longer without attention. An alternative to buying the (quite expensive) kit is to ask a specialist to do this for you. I think you would find the cost to be about the same. I had to have one done on a car manifold recently and the garage brought in a chap to do it rather than do it their self. About £60 if I remember and that was with the specialist coming to the vehicle.

Just To Add, I Had My 350 Done while its head was Off,
By a Local Car Engineering Works (Not a Garage) £15 a Plug Hole Insert`

Well Worth it, No Hassle...Give your local Motor works a Try....

Mind You the head was off to do a De-Coke at the time.....(1st Coke at 28 Thou Miles)

Cheers all...Craig

Thanks for all the advice guys. You've put my mind at rest. I was worried that a steel insert in an aluminium head might not be the best option and I wanted a long term solution that would still allow for heat dissipation. I had heard that I might need a hard anodized aluminium insert to do this, but it seems that steel will work. I think I'll probably just take the head off and try to do the job properly. Thanks once again for your help, and hopefully I'll be able to return the favour one day. Cheers.

A steel spring Helicoil insert will be fine, I've just bought a kit to do mine. Have used a borrowed one to Helicoil a couple of heads in the past. And they've been fine afterwards. I'd recommend you take the head off to do it, it's very straightforward on a single OHV, did a inline 4 on the barrels and it may be coincidence but the head gasket started weeping oil a couple of weeks after. Take it off, do it, clean it, refit, peace of mind. If you look on online internet bay you'll see Helicoil type kits for about 15 pounds with drill, tap and inserts

Hello there NAMGAZ-----------as an alternative to helicoiling have a look at this }----------------http://www.specialty-fasteners.co.uk/ca ... --Keensert are designed to be used especially in materials such as Alumunium etc plus there's no little tang to break off. Incidentally, from someone who used this product on a daily basis ( Disclaimer )---as it's only soft Alumunium swarf that might drop into the cylinder you can blow this out with a compressed air gun through the open exhaust valve. Any remainder gets a much stronger blast when you start the engine. Worked for me. OR }---- as mentioned, if your mileage/situation requires it then a head removal is not that difficult at all. Horses for courses really.

I had a search around for those Alan when you mentioned them. They are unfortunately, extortionate for the hobbyist, especially when it may get 1 use then sit on a shelf in the shed for years.
Shame as they do look excellent and I like the locking idea. That's why I went with the Helicoil type.